Hey, thanks for all the kind messages- it means a lot to me. Life can be shit at times but I'm learning to be more positive (or that's the theory anyway). I can be such a negative depressing person at times.

The diy synth thing is great therapy. It takes ones mind from the troubles of life. It teaches us patience. Builds confidence. There are some really smart people on this forum. Everything I have learnt in this field has come from this site and I'm grateful of that. I'm a great believer in informal education. You can teach yourself anything if you really want to. It's easy to look at that 2014 build pictures thread and scroll past those photos. But there is a lot of work in each of those builds, and years of knowledge in many. I'm in awe.

I'm looking at all my bagged up boards tonight, which is a good start. I'm going to try get back to this next week. Keep on building everyone! It's a damn good hobby.

Mhh it doesn't comes from the jack, other modules are clean with the same jack, it's not a ground loop. What i here is a constant noise coming from the snare. It's weak but enough to disturb me, it's a bit noisy. I think there's something to adjust in the noise part, the pot is ok so maybe some resistors in the noise part circuit.

So, here's the schematic for the snare. Obviously the standalone stripboard has its own white noise generation as well, that comes into this circuit in the lower right and into the base of Q48.

If you have the level (VR7) *all the way down* and you're still getting the noise generator's output, then you're likely getting inductive coupling between the trace that goes from the white noise to Q48 and the trace that goes from the op amp tot he 1K resistor and out to the wiring going to the jack.

Question: does the snappy control affect the sound of the bleed in the output? If so, then it's not that initial trace, but some other trace within that "snappy" section in the bottom center.

I don't see the SD stripboard in this thread, so I don't know which one you're working from to speculate further. I've never had a lot of luck finding old stuff on these forums, even when I know it's out there somewhere. My own SD that I mentioned above in this thread was built on protoboard rather than stripboard, straight from the schematic.

As noted, I think your best first option is to get some shielded wire, ground the shield (on one end only) and run that in place of whatever wire you have running from the board to the jack. After that, you need to actually look at how things are routed on the stripboard.

So the noise path does not appear to run particularly close to the output path, BUT both the output op amp and the noise op amp are on the same chip, IC2, so that could be relevant.

C21 and C22 are the decoupling caps for that chips power supply, you might want to make sure they've got good solder joints. Measure the power supply pins and see if you are getting any extra noise there, and possibly increase the size of those two?

Hahaha ok i've just spotted something. I'm so stupid. The constant noise is normal i think, i worked with the level pot (the volume, not the noise) all the way up. The output volume was low. I did it for compensate the low volume caused by the low trigger. I've a beatstep pro wich triggers almost everything. All the other modules are well triggered. But it seems that in this case the snare needs higher voltage to works correctly. With higher trigger, i've to lower the volume, and the noise problem disapears. So stupid... Sorry haha. In fact there's only one problem, the triggering. So maybe i have to change a resistor in the trigger part.

What are you putting into that? How do you have the trigger and accent hooked up when you're using the BSP?

Edit:

the BSP is supposed to send 10V gates which should be plenty high, but you might check the width of the trigger as well. Original circuit expects 1ms triggers on the accent input and wider than that for the "trigger" input. (Long story, ask if you like )

Well, after few hours... A 220ohm instead of 10K in the trigger section... LOL.
Everything works fine now.
I've found some differences between the original version and Eric Archer's one, I thought TRIG and ACCENT were inverted.Last edited by lysergist on Wed Jun 01, 2016 4:57 pm; edited 1 time in total

The way the original worked, the sequencer itself was done by a microprocessor.

There was a common trigger bus that went to all voices all the time. This is the "TRIG" input you see in the picture I posted. The trigger was 1) 1ms wide and 2) varying height, depending on the setting of accent for the given clock step. If accent was not active it was 4V or so. If it was active, it would vary from there up to 14V. How much it varied was set by the accent level pot.

So then you ask: why don't all the voices sound every single time?

Because there was a second input that was basically a "gate" for the voice. If you look at that schematic again, if the SD input is 0, then the NPN connected to it is off, and when the trigger comes through, there's no where for the voltage to flow. If it's on, then that transistor conducts, and the trigger comes in and effectively goes through a voltage divider that turns on the PNP transistor and actually injects the trigger into the voice.

So in the normal course of things, if the snare was to fire on "this step", the microprocessor would raise the gate for the snare, then generate the common trigger with it's accent level, then lower the gate.

When Eric Archer adapted the circuits for standalone voices, I think he felt it was more straightforward to make the accent a "level" input to the voice, and use a trigger in place of the gate. And in most cases that works just fine. On my own standalone 808 BD module I have normalled the trigger to the accent, but I could just as well have put it on the wiper of a pot doing voltage division.

I could definitely see how having a 220 in place of that 10K would be a problem .

That should work fine.... though you may want to put an additional resistor between the 50K and ground. Back of the envelope suggests about 15K should put the bottom side of the pot at 4V, which was the minimum the original circuit expected to be at the accent point.

Also, I don't think the stripboard layout you're working from has it, but you'll notice that Eric Archer's version also puts a gate -> trigger converter on the front end of the trigger input, to be sure that is just a pulse rather than a possibly extended gate (which won't respond the way you expect). If you're tying accent to a steady voltage, I think that's a good idea to do as well.

I put the four pieces that use the same noise source (cymbals, hats, cowbell) on two 4x5 stripboards.... it was doable, but just barely. I'd expect an 8x4 to be difficult at best without redoing significant bits. I haven't seen much bigger stripboard....

Awesome thread elmegil, I always wanted a TR808 cowbell! That and the long decay bass drum are the two most distinctively TR808 sounds.

Thanks for this I was looking for a project that could be built on strip board ( me + home made PCB = )

Will report back on my progress.

Just to add to an earlier part of the discussion; the threshold voltages in the Schmitt triggers in the 40106B, vary for devices from different manufacturers. So the resultant frequencies can vary from device to device, in some cases even with different devices from the same manufacturer. Consequently no two versions of these drum circuits will be identical.

I noted earlier in the thread that in some cases there were differences in the sound of the actual drum machines. This makes sense as the oscillator frequencies are highly dependent on the levels of these thresholds, which as I said, vary from device to device.

I found that the tuning of the two oscillators sounded better to my ears when tuned higher (I think) than the frequency specified. As for the other oscillators, they are contributing to the mix of what makes the noise or sound source. How important their frequency is, is anyones guess as only the frequency of the tuneable two are specified on the original schematics.

You could either go with a close value for the capacitors, or find some circuit emulator online to find the frequency with the specified components then substitute the caps and adjust the resistors to get the specified frequency.

Or I could get my board out and do some measurements with a scope. This last option may take a little while. My scope usage is rare and when I do need to use it, it takes several Youtube videos to jog my memory as to how to operate it. My boards are awaiting an enclosure still, but it's on its way. I have a huge backlog of completed boards but I have been building panels this year and enclosures... I can dig out the boards and measure each oscillator if need be.

Hi there,
I've come up with some data which might interest people here. Using the calculator here: http://www.talkingelectronics.com/pay/BEC-2/Page49.html I calculated the six schmitt trig oscillator frequencies from the original 808 schematics. Here they are, listed top to bottom. The ones with the range are the tuneable ones used for the CB.

147-362 Hz
208-666 Hz
303 Hz
177 Hz
214 Hz
119 Hz

I don't know if there are other considerations (aside from the feedback resistor value and the cap from the input to GND) when calculating the freq of a schmitt trig osc. If there are, these numbers are probably wrong...

That formula on the talking electronics site is only valid for certain makes of hex inverter, I've already confirmed this by actual measurements. In fact even chips from the same manufacturer, have parameters* that can vary around +/-20% rendering the formula only useful for giving ballpark figures, in other words to the nearest decade.

* The parameters in question are the higher and lower thresholds of the Schmitt trigger, these determine the points at which it switches between charging and discharging the capacitor in each oscillator. These are also affected by supply voltage, so in addition to the problem of the +/-20% variation, any formula would only be applicable at a certain supply voltage. It might be possible to derive a formula that takes all of this into account, but that sounds like too much of a headache to even consider!

You cannot post new topics in this forumYou cannot reply to topics in this forumYou cannot edit your posts in this forumYou cannot delete your posts in this forumYou cannot vote in polls in this forumYou cannot attach files in this forumYou can download files in this forum

Please support our site. If you click through and buy from our affiliate partners, we earn a small commission.